In conventional periodic antenna arrays, the radiating elements are of uniform size and are equally spaced one-half wavelength apart, in order to minimize the effects of grating lobes. In practice, array elements cannot be located closer together than one-half wavelength because the closer spacing results in increased mutual coupling which changes the aperture illumination of the antenna. There are two primary disadvantages of periodic arrays. First, the cost of the array is proportional to the number of array elements and second, undesired coupling occurs between closely spaced elements. By varying the interelement spacing, fewer radiating elements are needed, thus decreasing the cost of the array and minimizing the coupling effects. Since the array occupies the same preselected "aperture", while utilizing fewer elements, it is said to be a "thinned" array.
Periodic antenna arrays may be of the "inactive" or "active" type wherein each radiating element in an active array is driven by a power amplifier. In the past, it has been necessary to thin the array in order to dissipate the thermal heat generated by the amplifiers in the array.
Conventional techniques of aperture thinning rely on statistical random exclusion of radiating elements to achieve the characteristics of the conventional periodic array. The statistically thinned elements are of uniform size and randomly located. However, they are not uniformly random across the aperture. The average density of the elements is statistically computed based on a model amplitude taper of the conventional periodic array. The model amplitude taper specifies the probability that an element will be located at a particular position in the aperture. In the thinned array, an element is placed at a particular location if the value of the amplitude taper, at that location, is less than a predetermined number.
Although statistical thinning reduces the effects of grating lobes, because the elements are randomly located, it can only be used with radiating elements of the same size. Furthermore, statistically thinned arrays are complicated to build because they are not uniformly designed.
The present deterministic thinned phase array is intended to overcome each of the deficiencies of prior art mentioned above.